(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to improve the contact between a metal interconnect structure, and an underlying conductive plug structure, located in a via hole.
(2) Description of Prior Art
Micro-miniaturization, or the use of sub-micron features, has allowed the semiconductor industry to improve device density, resulting in improvements in device performance, and reductions in processing costs for a specific semiconductor device. The sub-micron features have in part been obtained via advancements experienced in the photolithographic discipline, such as the use of more advanced exposure tools, as well as the development of more sensitive photo sensitive materials. The use of sub-micron features can however in some cases, give rise to yield and performance degradations, not encountered with counterpart devices fabricated using larger features. For example the situation in which an upper level metal interconnect structure is designed to overlay, and contact, a portion of a metal plug structure, located in a via hole, which in turn allows electrical communication between the upper level metal interconnect structure, and a conductive region, underlying the metal plug structure, can be adversely influenced by sub-micron features, as well as by shrinking ground rules. The margin or error, encountered via misalignment of the upper level metal interconnect structure to a portion of the metal plug structure, may be difficult to contain when employing the sub-micron features achieved using advanced photolithographic procedures. This type of mis-alignment can lead to high resistance, performance problems, or even yield degrading opens, between metal interconnect structures.
This invention will describe a novel process sequence which allows self-alignment, and greater contact between metal interconnect structures, connected by a recessed metal plug in a via hole. Prior art such as Lee et al, in U.S. Pat. No. 5,956,609, as well as Wang et al, in U.S. Pat. No. 5,994,213, describe methods used to fabricate metal plug structures, however these prior arts do not described the metal ring structure, on a recessed plug structure located in a via or a contact hole, featured in this present invention.